This invention is concerned with drying solid bulk materials, such as plastic pellets, powders or other particulates.
Commonly owned U.S. Pat. No. 6,289,606 issued Sep. 18, 2001 and U.S. Pat. No. 6,584,701 issued Jul. 1, 2003 disclose systems and methods for drying particulate material in a hopper using heated gas, both patents being incorporated herein by reference.
In U.S. Pat. No. 6,289,606, dehumidified air from a dessicant bed is supplied to a hopper and is returned from the hopper to the dessicant bed. When the dew point of the return air drops to a pre-set level, a diverter causes the return air flow to bypass the dessicant bed and to be re-supplied to a hopper without dehumidification.
In U.S. Pat. No. 6,584,701, air from a compressed air inlet flows through a membrane dryer and a heater and is supplied to a lower portion of a dual flow hopper. Another portion of the air from the inlet is mixed with air extracted from the hopper. The mixed air flows through a heater and is supplied to a higher portion of the hopper.